May 2015: The key ingredient for healthy soils and healthy crops is soil organic matter. But it has been neglected in recent decades. How could we have forgotten about it? And what is needed to bring it back in the fields and on political agendas?
We know that soil health and soil fertility are essential in maintaining plant, animal, and human health, and therefore for food security and food sovereignty. Soil health depends on organic matter which contributes to its capacity to retain water and nutrients, and feeds soil life.
Why did we forget about organic matter?
Before the 1940s, organic matter was a key theme at international soil conferences. There is decade-old, almost forgotten wealth of knowledge about organic matter. But things changed after the Second World War. Organic matter became neglected, and not by accident. The process of artificially producing nitrogen was originally developed for the explosives industry, but then the resulting chemical was also used for fertilizer. The impact on maize yields was so dramatic that researchers and policy makers became convinced that chemical fertilizer could solve global hunger.
With this new emphasis on chemical fertilizers, world renowned researchers working on soil organic matter were systematically neglected. Scientific journals were no longer interested in publishing their research, and they were no longer invited to international conferences. Subsequently, the importance of soil organic matter also dropped off agricultural curricula and from policy, extension and investment agendas.
Under the influence of the economic and political power of the chemical industry (an influence that still exists today), new crop varieties and production methods that required large quantities of fertilizer were promoted. Slowly then, this belief, pushed by industry, narrowed the view of researchers, education, policy makers and extension staff and became the norm. Chemical fertilizers were so much easier to apply a few bags of fertilizers than the bulky organic matter that also demanded mixed farming. But sole addition of chemical fertilizers to soils, without also adding organic matter causes major problems, as also explained by Roland Bunch.
The trend towards simplification, away from mixed farming and specialising in either livestock or crops, gave further currency to this narrow approach to soil fertility management. In the 90s, this combined with other challenges of globalization including an increase in industrial mining, logging and oil production, which led to more pollution and degradation. Agroecological methods for building and maintaining a healthy, living and resilient soil were largely forgotten or made impossible.
With the use of chemical fertilizers and new varieties, crop yields first increased in some parts of the world. But now, many farmers are experiencing diminishing returns. They need to apply more and more (expensive) fertilizer each season (see ‘Keeping composting simple’). This is largely due to the loss of soil organic matter and loss of its capacity to retain water and nutrients. Pollution from excess nutrients and eroded soil particles entering waterways are additional long-term consequences of this historical mismanagement.
And, was hunger eliminated, or even reduced, in the process? The total food production per capita increased but there aremore hungry and malnourished people today than ever in the history of humanity. This shows that hunger is a not a production problem. There is food enough for all but it does not reach the poorest, while it’s estimated that 28% of the world’s agricultural area is used to produce food that is wasted.
With the globalisation of our food systems, we are also confronting a growing global imbalance. Nutrients are mined from the soil in one part of the world, and exported in the form of crops to other parts, leading to problems on both sides.
A new agenda for healthy soils
It is estimated that 17% of the land surface has been strongly degraded. So, it is high time that we revive soils with practices that increase organic matter and do not demand ever increasing amounts of non-renewable resources. These practices already exist around the world and we can draw a lot of inspiration from them. Farmers have worked with others to develop successful agroecological strategies using fallows, cover crops, green manures, mulch, and the incorporation of crop residues and compost into their living soils.
According to former Rapporteur on the Right to Food Olivier De Schutter, agroecological principles can increase crop yelds significantly: “Agroecological projects have shown an average crop yield increase of 80% in 57 developing countries” As described by Brazilian soil scientist Irene Cardoso, agroecological practices to improve soils lead to long-term productivity, and increase farmers’ resilience and autonomy.
To restore our soils, we must overcome a range of obstacles, from local shortages of biomass to lost knowledge and oversimplified systems. We must build on and learn from farmers and their existing agroecological practices. The International Year of Soils should build momentum to provide these practices with further support through policy and research. Then, we can work together with farmers to restore our soils so they are productive for generations to come.
What is organic matter?
Soil organic matter is made up of a wide variety of living and dead plant and animal material. In agriculture, this can range from leaf mulch to manure and compost. Often called ‘black gold’, it is a basic building block of soil life that supports plants to grow and thrive. It is important in several ways, mainly by enhancing soil life and increasing the water and nutrient holding capacity.
How does that work?
The process of ‘decay’ of organic matter is in fact a result of it being ‘consumed’ by the multitude of organisms in the soils, who then transfer its key component carbon into their own tissues or excrete it. These organisms range from millions of different species of fungi and bacteria, and insects and other arthropods, to larger creatures like earthworms that we know well.
This process also causes the breaking down and recombination of a range of compounds into forms that can be more readily absorbed by plant roots. This process is called mineralisation. It is key in nutrient cycling processes that help soils to produce healthy crops. Soil life also forms symbiotic relationships with plant roots, nitrogen is fixed and provided to plants in exchange for sugars, and nutrients such as phosphorus are solubilised for uptake by crops.
In short, soil organic matter improves soil structure, drainage and aeration; increases water and nutrient storage capacity; increases the activity and number of soil microorganisms and encourages macrofauna, such as earthworms and termites, which loosen soil and improves soil structure. And soil organic matter also plays a role in climate change mitigation. The more carbon that is incorporated in soils, as part of organic matter, the more CO2 that is fixed.